Olefin polymerization

ABSTRACT

A process is disclosed for the particle form polymerization of olefins. The process employs a titanium-containing having hydrocarbon soluble titanium components. The resulting catalyst is pretreated with an organometallic reducing agent prior to the introduction of the catalyst into the polymerization zone to give a catalyst which can be used satisfactorily in a loop reactor with lower levels of cocatalyst.

This application is a divisional of application Ser. No. 07/594,268,filed Oct. 9, 1990.

FIELD OF THE INVENTION

The present invention relates to the polymerization of olefins. In oneaspect the present invention relates to slurry or particle formpolymerization. In another aspect the present invention relates toolefin polymerization using a continuous loop-type reactor. In stillanother aspect the present invention relates to novel catalyst systemsfor use in the polymerization of olefins.

BACKGROUND OF THE INVENTION

One of the more common techniques employed for the polymerization ofolefins involves carrying the polymerization out in a liquid diluentunder conditions such that the polymer is formed in the forms of solidparticles such that the reaction product is a slurry of particulatepolymer solids suspended in a liquid medium. Such reaction techniqueshave been referred to as slurry or particle form polymerizations. Aparticularly desirable method for carrying out such particle formpolymerization involves the use of continuous loop-type reactors.Examples of such reactor systems are disclosed in U.S. Pat. Nos.3,152,872 and 4,424,341, the disclosures of which are incorporatedherein by reference.

In the past, many of the commercial particle form polymerizationprocesses have used chromium based catalysts. Such processes have,however, also been carried out using titanium based catalyst andorganometallic cocatalysts.

When using low levels of cocatalyst in the particle form polymerizationthe applicants have noted some problems in using a titanium basedcatalyst. Even though the levels of cocatalysts are high enough toensure sufficient productivity, it has been observed that with atitanium-containing catalyst system when the level of cocatalyst dropsbelow a certain level there is a tendency for a skin of some type toform within the reactor walls inhibiting heat transfer. On bench scaleunits where the polymerization is only an hour or so long and where heattransfer is usually not critical the phenomena is usually not observed.However, in commercial scale polymerizations, particularly in loopreactors the phenomena has been observed.

The exact nature of this skin formation is not understood at this time.It has been theorized by the applicants that it may be due to theformation of soluble polymer or soluble catalyst. One theory of theapplicants is that it may actually be due to the bleeding off ofhydrocarbon soluble species from the catalyst.

An object of the present invention is to provide a method for theparticle form polymerization of olefins using a titanium containingcatalyst system with a reduced tendency to cause the formation of a skinduring the polymerization.

Another object of the present invention is to provide a process for theparticle form polymerization of olefins using a titanium based catalystwhich can be employed satisfactorily with low cocatalyst levels.

Another object of the present invention is to provide a titaniumcatalyst which can be used in a commerical scale particle formpolymerization without the employment of high levels of cocatalyst.

Other aspects, objects, and advantages of the present invention will beapparent to those skilled in the art having the benefit of the followingdisclosure.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided a method forthe polymerization of olefins which comprises contacting an olefin witha titanium-containing catalyst under particle form polymerizationconditions in a polymerization zone wherein said catalyst is prepared bycontacting a particulate titanium-containing catalyst having hydrocarbonsoluble titanium components with an organometallic reducing agent priorto the introduction of the catalyst into the polymerization zone.

In accordance with another aspect of the present invention there isprovided a catalyst for the polymerization of olefins. The catalyst isprepared by contacting a particulate titanium-containing catalyst havinghydrocarbon soluble titanium components with an organometallic reducingagent prior to the introduction of the catalyst into the polymerizationzone.

In accordance with a particularly preferred embodiment thetitanium-containing catalyst is prepared by contacting a titaniumalkoxide and a magnesium dihalide in a suitable liquid to produce asolution, the solution is contacted with a suitable precipitating agentto obtain a solid, the solid after possible being contacting with olefinto form prepolymer is contacted with titanium tetrachloride, and thenthe resulting solid is contacted with a hydrocarbyl aluminum compoundprior to the introduction of the solid into a polymerization vessel.

DETAILED DESCRIPTION OF THE INVENTION

It is considered that this invention would have application for anyparticle form polymerization when the catalyst is a titanium-containingcatalyst which contains hydrocarbon soluble titanium components. A widerange of such titanium-containing catalysts are known. Some examples ofsuch catalysts include those disclosed in U.S. Pat. Nos. 4,477,586;4,394,291; 4,325,837; 4,326,988; 4,363,746; 4,329,253; 4,618,661;4,626,519; 4,555,496; 4,384,982; 4,406,818; and 4,384,982; thedisclosures of which are incorporated herein by reference. For thepurpose of this disclosure a catalyst is deemed to be a catalystcontaining hydrocarbon soluble titanium components if the titaniumcomponents are soluble when the catalyst is placed in a C₄ to C₈hydrocarbon at a temperature in the range of 0° C. to 110° C.

The organometallic reducing agent that is contacted with thetitanium-containing solid catalyst can be selected from generally any ofthose type of organometallic reducing agents that have in the past beenused as cocatalysts with such titanium-containing catalysts. Examplesinclude organometallic compounds such as hydrocarbyl aluminum compounds,hydrocarbyl boron compounds, and hydrocarbyl alkali or alkaline earthmetal compounds. Some specific examples of such reducing agents includetriethylboron, diethylmagnesium, diethylzinc, n-butyl lithium, and thelike. The currently preferred organometallic reducing agent is selectedfrom compounds of the formula R_(m) AlZ_(3-m) wherein R is a hydrocarbylgroup having 1 to 8 carbons, Z is a halogen, hydrogen, or hydrocarbylgroup having 1 to 8 carbons, and m is a number in the range of 1 to 3.The currently most preferred organometallic reducing agents are selectedfrom trialkylaluminum compounds, especially triethylaluminum.

The amount of reducing agent employed in pretreating thetitanium-containing catalyst can vary over a wide range. The optimumamount needed for the best overall improvement in the particle formpolymerization can be determined by routine experimentation. Generally,excess organometallic reducing agent can be used; however, in such casesit is desirable to subject the resulting product to a number of washeswith a hydrocarbon solvent to assure that soluble organometallicreducing agent is removed from the catalyst prior to the introduction ofthe catalyst into the polymerization process.

The invention is particularly useful when applied to atitanium-containing catalyst containing olefin prepolymer of the typedisclosed in U.S. Pat. No. 4,325,837. Such catalysts are prepared byreacting a titanium alkoxide with a magnesium dihalide in a suitableliquid to form a solution. The resulting solution is then contacted witha suitable precipitating agent and the resulting solid is contacted withtitanium tetrachloride either before or after prepolymer of an olefin isadded to the solid.

Examples of the titanium alkoxides include the titanium tetraalkoxidesin which the alkyl groups contain 1 to about 10 carbon atoms each. Somespecific examples include titanium tetramethoxide, titanium dimethoxidediethoxide, titanium tetraethoxide, titanium tetra-n-butoxide, titaniumtetrahexyloxide, titanium tetradecyloxide, titanium tetraisopropoxide,and titanium cyclohexyloxide.

The magnesium halide is preferably selected from magnesium chlorides.

The titanium alkoxide and the magnesium dihalide can be combined in anysuitable liquid. Examples include substantially anhydrous organicliquids such as n-pentane, n-hexane, n-heptane, methylcyclohexane,toluene, xylenes, and the like.

The molar ratio of the transition metal compound to the metal halide canbe selected over a relatively broad range. Generally, the molar ratio iswithin the range of about 10 to 1 to about 1 to 10, preferably betweenabout 3 to 1 to about 0.5 to 2; however, more often the molar ratios arewithin the range of about 2 to 1 to about 1 to 2.

Generally, it is necessary to heat the liquid mixture to obtain asolution. Generally, the components are mixed at a temperature in therange of about 15° C. to about 150° C. The mixing could be carried outat atmospheric pressure or at higher pressures.

The time required for heating the two components is any suitable timewhich will result in a solution. Generally, this would be a time withinthe range of about 5 minutes to about 10 hours. Following the heatingoperation, the resulting solution can be filtered to remove anyundissolved material or extraneous solid, if desired.

The precipitating agent is selected from the group consisting oforganometallic compounds in which the metal is selected from the metalsof Groups I to III of the Mendelyeev Periodic Table, metal halides andoxygen-containing halides of elements selected from Groups IIIA, IVA,IVB, VA, and VB of the Mendelyeev Periodic Table, hydrogen halides, andorganic acid halides of the formula R'-C-X wherein R' is an alkyl, aryl,cycloalkyl group or combinations thereof containing from 1 to about 12carbon atoms and X is a halogen atom.

Some specific examples of such precipitating agents include lithiumalkyls, Grignard reagents, dialkyl magnesium compounds, dialkyl zinccompounds, dihydrocarbyl aluminum, monohalides, monohydrocarbyl aluminumdihalides, hydrocarbyl aluminum sesquihalides, aluminum trichloride, tintetrachloride, silicone tetrachloride, vanadium oxytrichloride, hydrogenchloride, hydrogen bromide, acetyl chloride, benzoyl chloride, propionylfluoride, and the like.

The amount of precipitating agent employed can be selected over arelatively broad range depending upon the particular activities desired.Generally, the molar ratio of the transition metal of thetitanium-containing solid component to the precipitating agent is withinthe range of from about 10 to 1 to about 1 to 10 and more generallywithin the range of about 2 to 1 to about 1 to 3.

In especially preferred embodiments the catalyst contains an amount ofprepolymer sufficient to improve the particle size of the catalyst andultimately the size of the polymer particles produced in apolymerization reaction.

One way of forming prepolymer involves conducting the precipitation inthe presence of an aliphatic mono-1-olefin. Another technique involvescontacting the precipitated solid with an aliphatic mono-1-olefin undersuitable conditions to form prepolymer. This can be done either beforeor after the solid is treated with titanium tetrachloride. Examples ofolefins which can be used for forming prepolymer include ethylene,propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 4-methyl-1-pentene,1-heptene, 1-octene, and the like and mixtures of one or more thereof.The weight of prepolymer based on the total weight of the prepolymerizedcatalyst is generally in the range of from about 1 to about 90 wt. %,more preferably about 1 to about 20 wt. %, and still more preferablyabout 1 to about 15 wt. %.

The relative ratios of the titanium tetrachloride to the solid can varyover a wide range; however, as a general rule, the weight ratio of thetitanium tetrachloride to the prepolymerized or unprepolymerized solidwould generally be within the range of about 10 to 1 to about 1 to 10,more generally about 7 to 1 to about 1 to 4.

The pretreatment of the titanium-containing catalyst with anorganometallic reducing agent prior to the introduction of the catalystinto the polymerization zone is preferably carried out in asubstantially inert liquid, generally a hydrocarbon. The termorganometallic reducing agent as used herein refers to generally thosesame type of organometallic reducing agents that have been used in thepast as cocatalysts for transition metal based olefin polymerizationcatalysts systems. As noted above a preferred type of reducing agentincludes organoaluminum compounds such as triethylaluminum,trimethylaluminum, diethylaluminum chloride, ethylaluminum dichloride,ethylaluminum sesquichloride, methylaluminum sesquichloride,triisopropylaluminum, dimethylaluminum chloride, tridecylaluminum,trieicosylaluminum, tricyclohexylaluminum, triphenylaluminum,2-methylpentyldiethylaluminum, triisoprenylaluminum, methylaluminumdibromide, ethylaluminum diiodide, isobutylaluminum dichloride,dodecylaluminum dibromide, dimethylaluminum bromide, diisopropylaluminumchloride, methyl-n-propylaluminum bromide, di-n-octylaluminum bromide,diphenylaluminum chloride, dicyclohexylaluminum bromide, methylaluminumsesquibromide, ethylaluminum sesquiiodide, and the like and mixturesthereof.

Preferably conditions are employed in all the catalyst preparation stepsto minimize the presence of oxygen and water. The contacting can becarried out over a broad range of temperature conditions. Typically, thecontacting would be conducted at a temperature in the range of about 15°C. to about 150° C., more typically, about 20° C. to about 100° C. afterthe contacting the mother liquor is generally decanted and the resultingsolids washed several times with a suitable liquid solvent such as ahydrocarbon.

The amount of organometallic reducing agent employed can vary over abroad range. Excess organometallic reducing agent can be employed.Generally the organometallic reducing agent would be used in an amountsuch that the molar ratio of the reducing agent to the titanium in thecatalyst to be treated is in the range of about 0.01:1 to about 10:1,more preferably about 0.02:1 to about 3:1.

The resulting pretreated catalyst may if desired be mixed with aparticulate diluent such as, for example, silica, silica-alumina,silica-titania, magnesium dichloride, magnesium oxide, polyethylene,polypropylene, and poly(phenylene sulfide), prior to the use of thecatalyst in a polymerization process. The weight ratio of theparticulate diluent to the catalyst can be varied over a wide range.Typically, the weight ratio of the particulate diluent to the catalystis generally within the range of about 100 to 1 to about 1 to 100, ormore often in the range of about 20 to 1 to about 2 to 1. The use of aparticulate diluent has been found to be particularly effective infacilitating the controlled charging of the catalyst to the reactor.

The pretreated catalyst can be used in the polymerization of a varietyof polymerizable compounds. It is particularly useful for thehomopolymerization or copolymerization of mono-1-olefins. Olefins having2 to 18 carbon atoms would most often be used. The pretreated catalystis particularly useful in slurry or particle form polymerizationprocesses. In particle form polymerization processes the temperature andpressure conditions are generally selected to assure that polymer can berecovered as discreet particles. Typically, this would involvetemperatures in the range of about 60° to about 110° C. More generally,about 80° to about 110° C. The inventive pretreated catalyst isparticularly useful in situations where the cocatalyst istriethylaluminum and the level of triethylaluminum used in thepolymerization is less than about 25 ppm, based upon the weight of theliquid diluent used in the polymerization, more preferably thetriethylaluminum is used at a level in the range of about 5 to about 10ppm based on the weight of the liquid diluent used in thepolymerization.

In a continuous process, for example, a suitable reactor such as a loopreactor is continuously charged with suitable quantities of liquiddiluent, catalyst, cocatalyst, polymerizable compounds and hydrogen, ifany, in any desirable order. The reactor product is continuouslywithdrawn and the polymer recovered as appropriate, generally byflashing the liquid diluent and unreacted monomers and drying andrecovering the resulting polymer.

The olefin polymer is produced with this invention can be used inpreparing articles by conventional polyolefin processing techniques suchas injection molding, rotational molding, extrusion of film, and thelike.

A further understanding of the present invention and its objects andadvantages will be provided by the following examples:

EXAMPLE I Catalyst Preparations

Under a nitrogen atmosphere n-hexane, dry MgCl₂ and titaniumtetraethoxide, Ti(OEt)₄ were combined. The stirred mixture was heated to100° C. and held at this temperature for one hour. The mixture wascooled to 26° C. ethylaluminum dichloride (EADC) as a 25 wt. % solutionin n-hexane was added to the stirred reaction mixture over a period ofsixty minutes. After an additional 30 minutes, stirring was discontinuedand the solids allowed to settle. The solids were washed and decantedwith dry n-hexane followed by successive washing and decantation withtwo additional portions of dry n-hexane.

The reactor contents were then treated at ambient temperature withethylaluminum dichloride (EADC) as a 25 wt. % solution in n-hexane. Theaddition of the EADC solution to the stirred reaction mixture requiredabout 30 minutes.

Then ethylene was added to the reactor at ambient temperature bypressuring and repressuring an ethylene metering tank, to formpolyethylene (prepolymer) on the catalyst in the reactor. The reactorwas purged of ethylene with nitrogen and the "prepolymerized" catalystwas washed and decanted successively with two portions of dry n-hexane.Finally, dry n-hexane was added to the reactor.

Then titanium tetrachloride was gradually added to the reaction mixtureand the system was stirred for one hour at about 25° C. After the solidswere allowed to settle, the mother liquor was decanted and the solidswere washed and decanted with dry n-hexane. The solids were then washedand decanted successively with four additional portions of dry n-hexane.The catalyst slurry in dry n-hexane was transferred under nitrogen to astorage tank.

Two identical catalyst preparations gave about 402.5 lb of catalystslurry in dry n-hexane for use in the inventive pretreatment of thecatalyst with triethylaluminum (TEA).

A 20 lb sample of the catalyst slurry (15.57% solids containing 7.4 wt.% Ti) under nitrogen was transferred from the storage tank to thereactor and stirred for 10 minutes at ambient temperature. A 0.75 lbquantity (3.0 moles) of triethylaluminum was added to the reactor as afive pound portion of a 15 wt. % n-hexane solution and the stirredreaction mixture was heated to 50° C. After two hours at 50° C., thesystem was cooled to 30° C. and the mother liquor decanted. The solidswere washed and decanted successively with four 5 gal. portions of dryn-hexane before transferring the treated catalyst as a hexane slurryinto a storage tank. The estimated molar ratio of aluminum (from addedtriethylaluminum) to titanium present in the catalyst was about 3:2.2.This TEA pre-treated catalyst will be referred to herein as Catalyst A.

Another catalyst was prepared by reacting dry magnesium chloride withtitanium tetraethoxide in a hydrocarbon diluent and then reacting themixture with ethylaluminum sesquichloride to produce a solid. Ethyleneprepolymer was then formed on the solid. A hydrocarbon slurry of theresulting prepolymerized catalyst was then contacted with triethylaluminum (TEA) to give a pre-activated, pre-polymerized catalyst. Thiscatalyst will be referred to as Catalyst B.

EXAMPLE II

Pilot plant runs with the inventive TEA-pretreated Catalyst B werecarried out at reduced triethylaluminum levels in a loop reactor. Thisis one of the catalysts prepared using ethylaluminum sesquichloriderather than ethylaluminum dichloride. A summary of four inventive runsdirected toward the production of polyethylene is presented in Table I.The levels of TEA in the loop reactor for runs 1, 2, 3 and 4 were,respectively, 22, 10, 5 and 5. The normal level of TEA required in aloop reactor with untreated catalyst is much higher, viz., in the rangeof 25-150 ppm TEA. With an untreated catalyst, the use of TEA at levelsbelow 25 ppm causes fouling of the loop reactor.

Pilot plant runs were conducted in a liquid full 23 gal. loop reactorcontaining isobutane as a diluent. Effluent was periodically dischargedfrom the reactor and passed to a flash chamber where the polymer wasrecovered, dried and sieved. Diluent was intermittently charged to thereactor along with catalyst and with a dilute solution oftriethylaluminum in n-hexane to maintain desired levels of TEA andproductivity. Hydrogen was used as a molecular weight modifier for thepolymer. Circulation in the reactor was accomplished by means of anagitator operating at 1850 RPM in each run. The reactor temperature inruns 1, 2, 3 and 4 was 180° F. In order to facilitate feeding of thepretreated catalyst through the standard ball-check feeders, theTEA-pretreated catalyst was diluted with 5 parts calcined (200°-300° C.)silica per part of catalyst.

                  TABLE I                                                         ______________________________________                                        2-Day Continuous                                                              Pilot Plant Polyethylene Runs With TEA-Pretreated Catalyst                                   Run   Run     Run     Run                                                     1     2       3       4                                        ______________________________________                                        Hydrogen Concentration                                                                         1.35    1.50    2.23  2.14                                   (Mole Percent)                                                                H.sub.2 /C.sub.2.sup.=  Mole Ratio                                                             0.18    0.20    0.29  0.28                                   Triethylaluminum (ppm)                                                                         22      10      5     5                                      Polymer Melt Index                                                                             4.2     5.9     7.4   11.5                                   HLMI/MI.sup.a    35      36      38    37                                     Polymer Density (g/cc)                                                                         0.967   0.968   0.968 0.970                                  Flexural Modulus, MPa                                                                          1720    1800    1790  1830                                   Productivity     26,320  18,870  22,730                                                                              17,860                                 (g Polymer/g Catalyst/Hr)                                                     (excluding silica)                                                            Polymer Bulk Density                                                                           24.9    25.6    25.9  26.3                                   (lb/ft.sup.3)                                                                 ______________________________________                                         .sup.a HLMI/MI represents High Load Melt Index/Melt Index                

Referring to runs 1, 2, 3 and 4 in Table I it can be seen that atstart-up the TEA level in the loop reactor was 22 ppm (Run 1) and noreactor fouling was observed. After the reactor had lined out, the TEAlevel was reduced to 10 ppm and there was still no fouling problem (Run2). In runs 3 and 4 the TEA level was further reduced to 5 ppm TEA andno fouling was detectable. The total operating time represented by Runs1-4 in Table I was two days, i.e., these runs represent two days ofcontinuous operation in the pilot plant over the inventiveTEA-pretreated catalyst at reduced levels of TEA in the reactor loopduring which time no reactor fouling was detectable.

Other parameters in Table I do not appear to be significantly altered bythe lower TEA levels. The activity of the catalyst was relativelyconstant. Since the hydrogen concentration was increased during theseries, a slight decrease in activity would be expected. The increasinglevels of hydrogen would likewise cause increases in melt index. Thebreadth of molecular weight distribution reflected by the HLMI/MI valueswas essentially constant. The relatively higher HLMI/MI values were mostlikely caused by the relatively low reactor temperature (180° F.) ratherthan the lower TEA levels. Flexural modulus and bulk density values didnot change with TEA level. In general, the system did not respond in anegative manner to the reduced levels of TEA.

EXAMPLE III

The results of pilot plant runs covering three days of continuousoperation using Catalyst A are summarized in Table II. In order tofacilitate feeding of the inventive pretreated catalyst, theTEA-pretreated catalyst was diluted with 600° C. calcined silica. Theexact dilution rate was not known but was considered to be in the rangeof about 3 to about 5 parts by weight silica to 1 part by weight ofCatalyst A. The reactor temperature in runs 5, 6, 7, 8, 9 and 10 was190° F. The TEA levels in these runs were, respectively, 11, 10, 10, 12,9 and 8.

                  TABLE II                                                        ______________________________________                                        3-Day Continuous                                                              Pilot Plant Copolymer Resin Runs With TEA-Pretreated Catalyst                        Run   Run     Run     Run   Run   Run                                         5     6       7       8     9     10                                   ______________________________________                                        Hydrogen 1.56    1.53    1.57  1.37  1.64  2.18                               Concentra-                                                                    tion (Mole                                                                    Percent)                                                                      H.sub.2 /C.sub.2.sup.=                                                                 0.18    0.21    0.21  0.17  0.21  0.29                               Mole Ratio                                                                    Triethyl-                                                                              11      10      10    12    9     8                                  aluminum (ppm)                                                                1-Hexene, Wt %                                                                         0       3.3     3.4   15.0  14.9  14.9                               of Ethylene                                                                   Polymer Melt                                                                           4.2     15.2    18.2  14.5  19.7  27.2                               Index                                                                         HLMI/MI.sup.a                                                                          37      29      18    21    42    30                                 Polymer  0.968   0.967   0.966 0.960 0.960 0.961                              Density                                                                       (g/cc)                                                                        Flexural 1689    1770    1671  1515  1472  1563                               Modulus,                                                                      MPa                                                                           Productivity                                                                           2040    2040    2040  2080  1520  1890                               (g Polymer/g                                                                  Catalyst/Hr)                                                                  (including                                                                    silica)                                                                       Polymer Bulk                                                                           23.1    23.5    23.8  22.1  22.8  24.5                               Density                                                                       (lb/ft.sup.3)                                                                 ______________________________________                                         .sup.a HLMI/MI represents High Load Melt Index/Melt Index                

Referring to runs 5, 6, 7, 8, 9 and 10 in Table II it can be seen thatthe TEA level in the reactor at start-up was 11 ppm and varied between 8ppm and 12 ppm over a 3 day period of continuous operation. During thisperiod there was no detectable fouling problem and activity wasessentially unchanged.

Referring to runs 6, 7, 8, 9 and 10 the effect of adding 1-hexene to thereactor can be seen. In general, the melt index increased as the1-hexene was increased. Density decreased with increasing 1-hexene andflexural modulus decreased as expected. The somewhat lower values ofHLMI/MI were most likely due to the higher reactor temperatures used inruns 6-10. Bulk density remained relatively constant at the lower TEAlevels.

The results in Table II show that the inventive TEA-pretreated catalystpermits the use of lower levels of TEA in the loop reactor during thecopolymerization of ethylene and 1-hexane. No reactor fouling wasdetectable during 3 days of continuous operation.

EXAMPLE IV

The results of pilot plant runs based on five days of continuousoperation using Catalyst A are summarized in Table III. In order tofacilitate feeding of the inventive pretreated catalyst, theTEA-pretreated catalyst was diluted with 600° C. calcined silica. Hereagain the dilution was at the rate of about 3 to about 5 parts by weightof silica per part by weight of Catalyst A. The reactor temperatures inruns 11, 12, 13, 14, 15 and 16 were, respectively, 180° F., 182° F.,189° F., 191° F., 191° F. and 191° F. The TEA levels in these runs were,respectively, 9, 5, 5, 4, 2 and 2.

                  TABLE III                                                       ______________________________________                                        5-Day Continuous                                                              Pilot Plant Copolymer Resin Runs With TEA-Pretreated Catalyst                        Run   Run     Run     Run   Run   Run                                         11    12      13      14    15    16                                   ______________________________________                                        Hydrogen 1.95    1.99    2.05  2.06  1.97  2.09                               Concentra-                                                                    tion (Mole                                                                    Percent)                                                                      H.sub.2 /C.sub.2.sup.=                                                                 0.24    0.26    0.27  0.31  0.25  0.27                               Mole Ratio                                                                    Triethyl-                                                                              9       5       5     4     2     2                                  aluminum (ppm)                                                                1-Hexene,                                                                              14.4    14.8    14.9  15.3  15.8  6.6                                Wt % of                                                                       Ethylene                                                                      Polymer  38      42.2    64    118.7 59.9  34                                 Melt Index                                                                    HLMI/MI.sup.a                                                                          24      NA.sup.b                                                                              15    NA.sup.b                                                                            NA.sup.b                                                                            NA.sup.b                           Polymer  0.960   0.959   0.960 0.959 0.958 0.962                              Density                                                                       (g/cc)                                                                        Flexural 1544    NA.sup.b                                                                              1498  NA.sup.b                                                                            NA.sup.b                                                                            NA.sup.b                           Modulus,                                                                      MPa                                                                           Productivity                                                                           3640    3610    4650  3030  3130  3450                               (g Polymer/g                                                                  Catalyst/Hr)                                                                  (including                                                                    silica)                                                                       Polymer Bulk                                                                           24.8    25.2    26.4  26.4  26.3  26.1                               Density                                                                       (lb/ft.sup.3)                                                                 ______________________________________                                         .sup.a HLMI/MI represents High Load Melt Index/Melt Index                     .sup.b NA represents Not Available                                       

Referring to runs 11, 12, 13, 14, 15 and 16 in Table III it can be seenthat the TEA level in the reactor at start-up was 9 ppm and wasgradually reduced down to 2 ppm over a 5 day period of continuousoperation. During this period there was no detectable fouling problemand activity was essentially unchanged.

The general comments made in the previous example relating to theresults summarized in Table II also apply to the results shown in TableIII. It should be noted that on decreasing the TEA level in the reactorloop to 0.5 ppm the activity dropped sharply and the operation wasterminated.

Since the overall drop in density was slight considering the relativelylarge amount of 1-hexene present, it can be concluded that the TEAtreatment did not significantly affect the comonomer incorporation, evenat lower reactor temperatures. It is noteworthy that, e.g., in run 14with very high hydrogen and very high 1-hexene, the melt index was avery high 118.7.

EXAMPLE V

The results of pilot plant runs based on ten days of continuousoperation using silica diluted Catalyst B are summarized in Table IV.Runs 17, 18, 19 and 20 are related to a first type of copolymer resinwhereas runs 21, 22 and 23 are related to a different type of copolymerresin. Higher reactor temperatures were used to duplicate conditionsroutinely used with an untreated catalyst. The reactor temperature usedin runs 17, 18, 19 and 20 was 215° F. whereas the reactor temperaturesin runs 21, 22 and 23 were, respectively, 205° F., 205° F. and 199° F.

                                      TABLE IV                                    __________________________________________________________________________    10-Day Continuous                                                             Pilot Plant Copolymer Resin Runs With TEA-Pretreated Catalyst                               Run Run Run Run Run Run Run                                                   17  18  19  20  21  22  23                                      __________________________________________________________________________    Hydrogen Concentration                                                                      1.0 0.86                                                                              0.86                                                                              0.92                                                                              0.48                                                                              0.55                                                                              0.05                                    (Mole Percent)                                                                H.sub.2 /C.sub.2.sup.=  Mole Ratio                                                          0.14                                                                              0.14                                                                              0.14                                                                              0.15                                                                              0.08                                                                              0.09                                                                              0.09                                    Triethylaluminum (ppm)                                                                      10  10  10  5   5   5   5                                       1-Hexene, Wt % of Ethylene                                                                  0.21                                                                              0.25                                                                              0.27                                                                              0.29                                                                              1.07                                                                              1.15                                                                              1.27                                    Polymer Melt Index                                                                          24  19  19  17  6   8   9                                       HLMI/HI.sup.a 14  26  15  25  16  27  28                                      Polymer Density (g/cc)                                                                      0.958                                                                             0.954                                                                             0.957                                                                             0.957                                                                             0.945                                                                             0.944                                                                             0.944                                   Productivity  5000                                                                              3510                                                                              3570                                                                              3080                                                                              4170                                                                              4000                                                                              4000                                    (g Polymer/g Catalyst/Hr)                                                     (including silica)                                                            Polymer Bulk Density                                                                        29.3                                                                              29.1                                                                              29.3                                                                              29.5                                                                              25.9                                                                              26.3                                                                              25.1                                    (lb/ft.sup.3)                                                                 __________________________________________________________________________     .sup.a HLMI/MI represents High Load Melt Index/Melt Index                     .sup.b NA represent Not Available                                        

Referring to runs 17, 18, 19 and 20 in Table IV it can be seen that theTEA levels in the reactor for production of one of the Phillipscommercial scale copolymers were, respectively, 10, 10, 10 and 5. Inruns 21, 22 and 23 for the production of the other Phillips commercialscale copolymer, the TEA level in the reactor was 5 ppm. Since highertemperatures were used in these runs relative to the copolymer runs ofTable II and Table III of the previous examples, bulk densities werehigher. Other reaction parameters and polymer properties were similar tothe conventional technology used for producing these copolymers withuntreated catalyst and higher TEA levels in the loop reactor.

The results shown in Table IV demonstrate the efficacy of the inventiveTEA-treated catalyst to provide systems which produce quality copolymerat reduced TEA levels in the loop reactor. These systems also were freeof fouling problems during a continuous operation period of 10 days.

EXAMPLE VI

A commercial scale titanium-containing catalyst was evaluated. Thecatalyst was prepared by contacting titanium tetraethoxide and magnesiumdichloride to obtain a solution, then contacting the solution withaluminum sesquihalide to obtain a precipitate, contacting theprecipitate with ethylene to form a prepolymer, then contacting theprepolymerized solid with TiCl₄, followed by a number of hydrocarbonwashes to remove soluble titanium components. It has been observed byapplicants that even though a plurality of hydrocarbon washes are usedin such catalyst preparations, as the catalyst ages the level of solubletitanium components increases.

Five separate portions of the commercial scale catalyst were subjectedto treatment with triethylaluminum under different conditions toevaluate the effect. In each case 3.5 lb. of the solid catalyst in ahexane slurry was charged into a reactor. After mixing for 10 minutes, a15 wt. % triethylaluminum heptane solution was charged to the reactor.The slurry was then taken to the chosen reaction temperature and mixedfor 2 hours. Thereafter the resulting solid was washed 5 times withhexane. The variables in the catalyst pretreatment are set forth inTable V.

                  TABLE V                                                         ______________________________________                                        Catalyst Pretreatment Conditions                                                            TEA      Reaction                                                             Solution Temperature                                            Catalyst      (lbs)    (°C.)                                           ______________________________________                                        C             5.0      60                                                     D             0.5      60                                                     E             0.5      20                                                     F             5.0      20                                                     D             2.75     40                                                     ______________________________________                                    

Hexane slurries of each of the catalysts and of the original untreatedcommercial scale Control catalyst were subjected to analytical tests todetermine the relative amounts of soluble titanium components. Theresults are set forth in Table VI.

                  TABLE VI                                                        ______________________________________                                        Analytical Results                                                                                    Dried Catalyst                                        Supernatant Liquid (ppm)                                                                              (wt. %)                                               Catalyst                                                                             Color     Al     Ti     Mg   Al   Ti   Mg                              ______________________________________                                        C      black     95.0   1.8    0.5  5.8  12.8 7.2                             D      lt. brown 0.2    4.5    0.1  2.3  14.1 7.4                             E      lt. brown <0.1   0.3    <0.1 2.4  14.0 7.6                             F      black     92.6   0.2    <0.1 5.2  12.8 6.9                             G      dk. brown 24.0   <0.1   <0.1 4.2  13.0 6.7                             Control                                                                              lt. brown 0.2    >1699.1                                                                              0.2  1.6  14.0 7.4                             ______________________________________                                    

Treatment of the Control catalyst slurry with TEA at differentconcentrations and temperatures resulted in soluble titanium levelsunder 5 ppm in all cases.

EXAMPLE VII

The effectiveness of the TEA treated catalysts of Example VI inpolymerization was then compared to that of the untreated Controlcatalyst.

A one gallon capacity reactor was used for the polymerization. Thereactor was prepared for each polymerization run by adding about oneliter of isobutane, heating to 110° C. for one hour, draining thereactor, and then flushing it with nitrogen free isobutane. Catalystslurry and TEA cocatalyst were added to the reactor. The reactor wassealed and hydrogen added. About 2 liters of isobutane was pressuredinto the reactor. Ethylene was then fed to the reactor continually overa one hour period so that constant pressure was obtained. At the end ofthe hour, the ethylene flow was stopped, and the reactor was vented. Thepolymer was collected, vacuum dried at 60° C., and weighed.

The polymerizations were run in 1.1 Kg of isobutane, 90 g 1-hexene, and0.5 cc of 15% by weight triethylaluminum in n-heptane at 90° C. and 324psig total pressure for one hour. The hydrogen was measured into thereactor in the amount of 25 psi from a 2.25 l vessel. Reactant molarratios were 0.7 hexene/ethylene and 0.05 hydrogen/ethylene at anethylene concentration of about 7 mole percent. The results aresummarized in Table VII.

                  TABLE VII                                                       ______________________________________                                                Productivity                                                                  (kg/g/hr)                                                                           From     From   MI    HLMI/  Den-                                    Cat-     Catalyst Ti     (g/10 MI     sity                               Run  alyst.sup.(a)                                                                          Weight   Analyses                                                                             min)  Ratio  (g/cc)                             ______________________________________                                        24   C        24       18     1.26  27.3   .9429                              25   D        23       20     1.68  27.4   .9443                              26   E        25       23     1.65  27.4   .9435                              27   F        21       18     1.62  27.0   .9433                              28   G        24       25     1.39  27.6   .9440                              29   Control  26       23 (25).sup.(b)                                                                      1.16  30.7   .9439                              ______________________________________                                         .sup.(a) Fluff bulk densities ranged only from 14.8-15.4 lbs/cu. ft.          .sup.(b) Calculated correcting for Ti in solution.                       

The data shows that the productivity and polymer molecular weights wereslightly reduced by the TEA treatment. The shear ratios, fluff bulkdensities, and densities of the polymers were not materially affected bythe treatment. The TEA treatment thus reduced the soluble Ti levels ofthe catalyst without any significant adverse effect on the polymerformed or the performance of the catalyst. By reducing the hydrogenlevels it should be possible to increase the molecular weights andproductivities to values very close to those obtained with the untreatedControl catalyst.

EXAMPLE VIII

Another sries of polymerizations were carried out using the various TEApretreated catalysts and the Control catalyst to determine whether theTEA pretreatment would affect the type of polymer fines produced. Thepolymerizations were run in 1.1 Kg of isobutane at 100° C. and 500 psigtotal pressure for 1 hour. Triethylaluminum, 0.5 cc of 15% by weightsolution in n-heptane, cocatalyst was used; hydrogen, 132 psi from a2.25 l vessel, was in the reactor. The hydrogen/ethylene molar ratio was0.36 at 6.05 mole percent ethylene. The results are summarized in TableVIII.

                  TABLE VIII                                                      ______________________________________                                                Productivity                                                                  (Kg/g/hr)                                                                           From     From                                                                 Catalyst Ti     MI      Fines                                   Run  Catalyst Weight   Analyses                                                                             (g/10 min.)                                                                           (%-100 Mesh)                            ______________________________________                                        30   C        12       9      109     2.98                                    31   D        11       12     161     2.50                                    32   E        15       13     121     2.38                                    33   F        11       9      147     3.75                                    34   G        11       8      207     2.50                                    35   Control  11       8.sup.(a)                                                                            192     2.29                                    ______________________________________                                         .sup.(a) Calculated correcting for Ti in solution.                       

The data show that the TEA pretreatment does not have any significantadverse effect upon the polymer fines.

EXAMPLE IX

Another series of polymerizations were carried out to evaluate the TEApretreated Catalyst G at different cocatalyst levels in theco-polymerization of ethylene and 1-hexene. The polymerizations were runin 1.1 Kg isobutane, 90 g 1-hexene, and variable levels of 15% by weighttriethylaluminum in n-heptane at 90° C. and 324 psig total pressure forone hour. Hydrogen, 25 psi from a 2.25 1 vessel, was also in thereactor. Reactant molar ratios were 0.7 hexene/ethylene and 0.05hydrogen/ethylene at an ethylene concentration of about 7 mole percent.The results are summarized in Table IX.

                  TABLE IX                                                        ______________________________________                                        Triethyl                                                                      Aluminum.sup.(b)                                                                            Productivity                                                                             MI        HLMI/MI                                    Run  (cc)    (ppm).sup.(c)                                                                          (kg/g/hr)                                                                              (g/10 min.)                                                                           Ratio                                  ______________________________________                                        36   3.0     286      10.0     3.78    27.4                                   37   1.5     143      10.8     2.52    26.2                                   38   0.5     48       25.0     1.39    27.6                                   39   0.5     48       21.3     1.74    28.3                                   40   0.25    24       14.4     0.99    30.7                                   41   0.15    15        3.9     1.19    26.8                                   42   0.10    10       ND.sup.(a)                                                                             ND      ND                                     ______________________________________                                         .sup.(a) ND = not determined.                                                 .sup.(b) TEA was 15% by weight in nheptane (density = 0.70 g/cc).             .sup.(c) PPM based on isobutane.                                         

The data shows that in the bench scale pot-type reactor the productivityin the copolymerization was decreased as the TEA cocatalyst level wasdecreased. The effect upon productivity is apparently more notable inthe bench scale reactor than in a loop reactor.

EXAMPLE X

Another series of catalysts were prepared to evaluate the effects ofother organometallic reducing agents.

The Control catalyst was prepared by forming a solution of titaniumtetraethoxide and magnesium chloride. The solution was contacted withethylaluminum dichloride to obtain a precipitate. Ethylene waspolymerized on the precipitate to form prepolymer. The resulting solidwas then washed with TiCl₄ and then with several hydrocarbon washes.

Separate portions of the resulting control catalyst slurried inhydrocarbon were contacted with different reducing agents, namelytriethylaluminum, diethylaluminum, triethylboron, diethylzinc,n-butyllithium, and Magala (a mixture of dibutylmagnesium andtriethyaluminum).

The effects of the various catalysts in the polymerization of ethylenewas then compared. The polymerizations were carried out in substantiallythe same manner as those described in Example VII. The variables andresults are summarized in Table X.

                  TABLE X                                                         ______________________________________                                             TEA     Hydrogen  Productivity                                                                           MI      HLMI/                                 Run  (cc)    (psi)     (Kg/g/hr)                                                                              (g/10 min.)                                                                           MI                                    ______________________________________                                        Control Catalyst                                                              43   0.1     45        6.0      0.48    36.4                                  44   0.25    50        20.7     1.02    29.5                                  45   0.5     45        33.6     1.35    29.7                                  46   1.0     45        41.2     1.24    29.7                                  47   2.0     35        41.2     1.28    31.8                                  48   4.0     35        43.1     1.32    31.5                                  49   6.0     30        39.5     1.20    30.0                                  TEA Treated Catalyst                                                          50   0.1     40        14.3     0.65    34.5                                  51   0.25    40        21.4     0.65    30.9                                  52   0.5     40        27.8     1.47    24.6                                  53   1.0     40        36.0     1.26    29.8                                  DEAC Treated Catalyst                                                         54   0.05    40        2.0      --      --                                    55   0.1     40        34.4     0.89    32.6                                  56   0.25    40        66.6     1.57    29.6                                  57   0.5     40        53.8     2.06    27.6                                  58   1.0     40        57.5     1.93    28.2                                  TEB Treated Catalyst                                                          59   0.5     45        51.4     1.98    28.2                                  DEZ Treated Catalyst                                                          60   0.5     45        33.8     1.58    28.8                                  MAGALA Treated Catalyst                                                       61   0.5     45        22.1     2.0     27.8                                  Butyllithium Treated Catalyst                                                 62   0.5     45        37.6     0.89    37.8                                  ______________________________________                                    

In Table X a dash indicates that no determination was made. The resultsof Table X demonstrate that a particulate titanium catalyst containingsoluble titanium components can be effectively treated with a wide rangeof organometallic reducing agents. It will be noted in many cases theproductivity of the organometallic reducing agent treated catalyst washigher than that of the control at a given cocatalyst level.Particularly notable are the triethylboron and diethylaluminum chloridetreated catalysts.

That which is claimed is:
 1. A process for preparing a solid particulateolefin polymerization catalyst comprising contacting a titanium alkoxideand a magnesium dihalide in a suitable liquid to produce a solution,contacting said solution with a suitable precipitating agent to obtain asolid, contacting said solid with titanium tetrachloride, before orafter an optional prepolymerization step, contacting the resulting solidwith an organometallic reducing agent, and washing the then resultingsolid with a hydrocarbon to remove hydrocarbon soluble material toresult in said particulate olefin polymerization catalyst.
 2. A catalystproduced by the process of claim
 1. 3. A process according to claim 1wherein said organometallic reducing agent is selected from hydrocarbylaluminum compounds, hydrocarbyl boron compounds, hydrocarbyl alkali oralkaline earth metal compounds, and hydrocarbyl zinc compounds.
 4. Aprocess according to claim 1 wherein said organometallic reducing agentis selected from compounds of the formula R_(m) AlZ_(3-m) wherein R is ahydrocarbyl group having 1 to 8 carbons, Z is a halogen, hydrogen, or ahydrocarbyl group having 1 to 8 carbons, and m is a number in the rangeof 1 to
 3. 5. A process according to claim 1 wherein said titaniumcatalyst is prepared by reacting a titanium alkoxide and magnesiumdihalide to form a solution; then reacting that solution with aprecipitation agent selected from organometallic compounds in which themetal is selected from Groups I to III of the Periodic Table, metalhalides and oxygen-containing halides of elements selected from GroupsIIIA, IVA, IVB, VA, and VB of the Periodic Table, hydrogen halides, andorganic acid halides to produce a precipitated solid, and thencontacting said solid with titanium tetrachloride.
 6. A processaccording to claim 5 wherein said catalyst contains 1 to 10 wt. % of anolefin prepolymer.
 7. A process according to claim 6 wherein said olefinprepolymer is deposited on said precipitated solid prior to the solidbeing contacted with the titanium tetrachloride.
 8. A process accordingto claim 7 wherein the organometallic reducing agent, is selected fromorganoaluminum compounds of the formula R_(m) AlZ_(3-m) wherein R is ahydrocarbyl group having 1 to 8 carbon atoms, Z is a halogen, hydrogen,or a hydrocarbyl group having 1 to 8 carbons, and m is a number in therange of 1 to
 3. 9. A process according to claim 8 wherein said catalystis prepared by reacting a titanium alkoxide and magnesium dichloride ina suitable liquid to form a solution, then reacting that solution with ahalogenated organoaluminum compound to produce a solid, contacting saidsolid with an olefin under conditions sufficient to form prepolymer onthe solid, and then contacting the resulting solid with titaniumtetrachloride.
 10. A process according to claim 9 wherein said titaniumtetrachloride treated catalyst is contacted with a trialkylaluminumcompound.
 11. A process according to claim 10 wherein saidtrialkylaluminum compound is triethylaluminum.
 12. A process accordingto claim 11 wherein said catalyst is prepared by reacting titaniumtetraethoxide and magnesium dichloride in a suitable liquid to form asolution, then reacting the solution with an organoaluminum compoundselected from ethylaluminum sesquichloride and ethylaluminum dichloride,contacting the solid with ethylene under conditions sufficient to formpolyethylene prepolymer, and then contacting the resulting solid withtitanium tetrachloride.
 13. A catalyst according to claim 12 whereinsaid organometallic reducing agent is a hydrocarbylaluminum compound.14. A catalyst according to claim 13 wherein said titanium alkoxide istitanium tetraethoxide, said magnesium dihalide is magnesium dichloride,said precipitating agent is an alkylaluminum halide, and saidhydrocarbylaluminum compound is a trialkylaluminum compound.
 15. Acatalyst according to claim 14 wherein said alkylaluminum halide isselected from ethylaluminum sesquichloride and ethylaluminum dichlorideand said trialkylaluminum compound is triethylaluminum.
 16. A catalystaccording to claim 15 containing about 1 to about 10 wt. % olefinprepolymer.
 17. A catalyst according to claim 16 in combination with asilica diluent.
 18. A catalyst according to claim 12 wherein saidorganometallic reducing agent is triethylborane.
 19. A catalyst systemcomprising:(1) a catalyst prepared by contacting titanium tetraethoxideand magnesium dichloride in a suitable liquid to produce a solution,contacting said solution with a precipitating agent selected fromethylaluminum sesquichloride and ethylaluminum dichloride to produce asolid, contacting the solid with an olefin to produce a prepolymerizedsolid, contacting said prepolymerized solid with titanium tetrachloride,contacting a hydrocarbon slurry of the resulting solid with atrialkylaluminum compound, and then recovering the resulting solidseparate from the reaction mixture; and (2) an organometalliccocatalyst.
 20. A catalyst system according to claim 19 wherein saidtrialkylaluminum compound is triethylaluminum.
 21. A catalyst systemaccording to claim 20 wherein said cocatalyst comprisestriethylaluminum.